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High-temperature, high-pressure (HTHP) describes wells where the bottom hole static temperatures (BHST) are at least 300°F. Such wells are not a new topic these days. For a decade, drilling fluid systems have been able to exceed what was traditionally considered HTHP into the realm of ultra-HTHP, meaning wells where the temperature is greater than 500°F. However, in the US Gulf of Mexico (GOM), Bureau of Safety and Environmental Enforcement (BSEE) defines HTHP as greater than 15,000 psi at the wellhead and greater than 350°F (Nannen 2020). For the first ever HTHP production project in the GOM to receive BSEE approval, reservoir drilling fluid (RDF) formulation was designed for deepwater use. It was formulated to withstand the temperature rigors of an over 350°F BHST. The lower intermediate section also exceeded the limit of the typical synthetic-based mud (SBM) systems used in the US GOM. A high performance, low-sag low-equivalent circulating density (ECD) drilling fluid system was redesigned into a new variant, extending the temperature stability to 340°F for prolonged static periods. Emphasis was placed on key testing parameters to ensure the drilling fluids would still meet performance requirements in a deepwater environment, while enhancing stability in the high temperature wells. Particular emulsifier packages and weight material were utilized to improve long term sag stability, with static aging stretching up to 28 days. Specialized fluid loss reducers were employed to maintain emulsion stability and tight filter cakes during extended HTHP testing at BHSTs over 350°F. This paper will explore the process of formulating drilling fluids for these HTHP drilling environments. From the laboratory to the field, this case study will carry through to results and lessons learned from the actual project execution. The drilling fluid systems deployed allowed the expansion of the drilling envelop in the GOM thus the access to new oil reserves. |
